Over the past decade, transgenic plants have been successfully used to express a variety of useful proteins. For example, production of proteases in plants has been achieved (See U.S. Pat. No. 6,087,558); along with production of aprotinin in plants (U.S. Pat. No. 5,824,870); and avidin (U.S. Pat. No. 5,767,379). A variety of mammalian bacterial and viral pathogen antigens are included in those proteins that have been successfully produced in plants, such as viral vaccines (U.S. Pat. No. 6,136,320), transmissible gastroenteritis and hepatitis vaccines (U.S. Pat. Nos. 5,914,123 and 6,034,298). These patents, as well as all references cited herein are incorporated herein by reference.
Many of the resulting peptides induced an immunogenic response in mice (Mason et al. (1998) Vaccine 16:13361343; Wigdorovitz et al. (1999) Virology 155:347-353), and humans (Kapusta et al. (1999) FASEB J. 13:1796-1799). After oral delivery, these vaccine candidates were immunogenic and could induce protection. Mice fed a basic diet plus corn expressing recombinant Escherichia coli heat-labile enterotoxin B-subunit (LtB) mounted a dose dependent IgG and IgA response (Streatfield et al. (2001) “Plant based vaccines—unique advances” Vaccine 19:2742-2748.) Some of the first edible vaccine technologies developed include transgenic potatoes expressing hepatitis B, TGEV and Norwalk virus antigens as well as various other viral antigens. (See, e.g., Thanavala et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92:3358-3361; U.S. Pat. No. 6,136,320; U.S. Pat. No. 6,034,298; U.S. Pat. No. 5,914,123; U.S. Pat. No. 5,612,487 and U.S. Pat. No. 5,484,719; Mason et al., (1996) Proc. Natl. Acad. Sci. 93:5335-5340; “VP1 protein for foot-and-mouth disease” (Wigdorovitz et al (1999) Virology 255:347-353)).
The utilization of transgenic plants for vaccine production has several potential benefits over traditional vaccine production methods. First, transgenic plants are usually constructed to express only a small antigenic portion of the pathogen or toxin, eliminating the possibility of infection or innate toxicity of the whole organism and reducing the potential for adverse reactions. Second, since there are no known human or animal pathogens that are able to infect plants, concerns with viral or prion contamination is eliminated. Third, immunogen production in transgenic crops relies on the same established technologies to sow, harvest, store, transport, and process the plant as those commonly used for food crops, making transgenic plants a very economical means of large-scale vaccine production. Fourth, expression of immunogens in the natural protein-storage compartments of plants maximizes stability, minimizes the need for refrigeration and keeps transportation and storage costs low. Fifth, formulation of multicomponent vaccines is possible by blending the seed of multiple transgenic plant lines into a single vaccine. Sixth, direct oral administration is possible when immunogens are expressed in commonly consumed food plants, such as grain, leading to the production of edible vaccines.
To be effective as a vaccine, the protein needs to be produced by the plant in a form that can elicit a protective response to a disease agent. This can be particularly challenging when the protein is a membrane-bound protein.